Conventional techniques for obtaining information about submerged features of objects (e.g., underwater pipes), such as techniques using acoustic sensors, are generally not capable of measuring relatively fine details, e.g., cracks. Because such details can be critical, however, attempts have been made to obtain more precise information about submerged surfaces of objects using laser scanning.
Conventional underwater laser measurement devices are known. However, such devices typically are only adapted to obtain two-dimensional point clouds of data, with the device remaining stationary. In order for the conventional measurement device to obtain three-dimensional data, the device is required to be moved from one known location to another known location.
Various types of underwater laser scanners have been described. For example, in “A Practical Underwater 3D-Laserscanner” (Hildebrandt et al., IEEE, 2008), a calibration system for a triangulation-based laser scanner is disclosed. In Hildebrandt et al., it is proposed that a laser scanner device (i.e., including a laser and a camera) may conveniently be assembled by mounting a laser on an underwater vehicle, where the vehicle includes a suitable underwater camera. After the laser is mounted on a vehicle to which a suitable camera has also been attached, a calibration procedure is followed, to ensure that the data provided by the laser scanner device provides accurate data. The calibration appears to be done in situ, which tends to be time-consuming and therefore costly. Also, the calibration in situ is required to be done repeatedly, i.e., every time that the prior art laser scanner device is mounted onto a different underwater vehicle.